1. Field of the Invention
The present invention relates to a safety hypodermic syringe and, more particularly, to a needle holder mounting arrangement for safety hypodermic syringe.
2. Description of Related Art
In a safety hypodermic syringe, the plunger has an arrowhead-like front tip adapted for hooking the needle holder, for enabling the needle holder and the needle cannula at the needle holder to be pulled backwards to the inside of the barrel to prevent contamination after the service of the safety hypodermic syringe. The needle holder is press-fitted into the inside of the front section of the barrel. However, when installing the needle cannula in the needle holder, the backward pressure from the needle cannula tends to force the needle holder out of position. Further, in order to prohibit the needle holder from escaping out of the barrel from the front side of the barrel, the barrel is made having a conical front end. This conical front end design prohibits the needle holder from forward movement relative to the barrel, however it facilitates backward movement of the needle holder in the barrel during installation of the needle cannula in the needle holder. In order to ensure positive positioning of the needle holder in the barrel, the friction-fit between the needle holder and the inside wall of the barrel is enhanced. However, enhancing the friction-fit between the needle holder and the inside wall of the barrel complicates the installation of the needle holder in the barrel. Further, an injection molding mold for molding needle holders or barrels for safety hypodermic syringe has multiple cavities. Because the injection environment (fluid material filling position, injection temperature, cooling speed, etc.) in each cavity is different, it is difficult to control the dimensions of the injection-molded finished products precisely. A small specification tolerance may cause the needle holder and the barrel unable to match each other perfectly.
Therefore, it is desirable to provide a needle holder mounting arrangement for safety hypodermic syringe that eliminates the aforesaid problems.
The main object of the present invention is to provide a needle holder mounting arrangement for safety hypodermic syringe, which prevents backward movement of the needle holder to the inside of the barrel accidentally. It is another object of the present invention to provide a needle holder mounting arrangement for safety hypodermic syringe, which is easy and inexpensive to manufacture.
To achieve these and other objects of the present invention, the needle holder mounting arrangement for safety hypodermic syringe comprises a barrel, a needle holder, and an expansion ring. The barrel comprises a fluid chamber. The fluid chamber has a front small inner diameter section, a rear big inner diameter section, and at least one locating means, for example, an inside annular locating groove in the inside wall of the front small inner diameter section. The needle holder comprises a front coupling section and a rear positioning section received in the front small inner diameter section of the barrel, a longitudinal center through hole axially extended through the front coupling section and the rear positioning section. The longitudinal center through hole has a rear receiving open chamber. The rear positioning section comprises at least one, for example, two side openings symmetrically disposed in the periphery thereof at two sides corresponding to the locating means, a plurality of movable positioning blocks respectively suspended in the side openings and partially projecting into the rear receiving open chamber of the longitudinal center through hole, and a plurality of springy connecting strip respectively connected between the rear end of the movable positioning blocks and the inside wall of the side openings. Each movable positioning block has a front inner hooked portion, and an outer protruded engagement portion adapted for engaging the locating means of the barrel. The expansion ring is press-fitted into the rear receiving open chamber of the needle holder to force the outer protruded engagement portion of each movable positioning block expanded outwards and engaged into the locating means of the barrel after insertion of the expansion ring into the rear receiving open chamber of the needle holder, stopping the needle holder from backward movement relative to the barrel accidentally. The expansion ring has a longitudinally extended center through hole, which is disposed in fluid communication with the longitudinal center through hole of the needle barrel.
After injection, the plunger of the safety hypodermic syringe is pushed forwards further to move the expansion ring to the front end of the rear receiving open chamber of the needle holder, for enabling the springy connecting strips to turn the movable positioning blocks inwards from the locating groove of the barrel and to force the positioning blocks into engagement with the arrowhead-like front retaining tip of the plunger so that the needle holder with the attached needle cannula are pulled backwards with the plunger and received inside the barrel upon back stroke of the plunger.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
FIG. 1 is an exploded view of the preferred embodiment of the present invention.
FIG. 2 is a sectional view of the preferred embodiment of the present invention before the connection of the expansion ring to the needle holder.
FIG. 3 is a sectional assembly view of the preferred embodiment of the present invention showing the expansion ring fitted into the rear end of the rear receiving open chamber of the needle holder.
FIG. 4 is a sectional view showing the action of the preferred embodiment of the present invention (I).
FIG. 5 is a sectional view showing the action of the preferred embodiment of the present invention (II).
FIG. 6 is a sectional view showing the action of the preferred embodiment of the present invention (III).